Re: [dpdk-dev] [PATCH v5 5/5] eal: simplify parameters of hotplug functions

[Thomas Monjalon <thomas@monjalon.net>]

04/10/2018 11:44, Gaëtan Rivet:
> On Thu, Oct 04, 2018 at 01:10:46AM +0200, Thomas Monjalon wrote:
> > --- a/lib/librte_eal/common/eal_common_dev.c
> > +++ b/lib/librte_eal/common/eal_common_dev.c
> > @@ -129,46 +129,61 @@ int rte_eal_dev_detach(struct rte_device *dev)
> >  
> >  int
> >  rte_eal_hotplug_add(const char *busname, const char *devname,
> > -		    const char *devargs)
> > +		    const char *drvargs)
> >  {
> > -	struct rte_bus *bus;
> > -	struct rte_device *dev;
> > -	struct rte_devargs *da;
> >  	int ret;
> > +	char *devargs = NULL;
> > +	int size, length = -1;
> >  
> > -	bus = rte_bus_find_by_name(busname);
> > -	if (bus == NULL) {
> > -		RTE_LOG(ERR, EAL, "Cannot find bus (%s)\n", busname);
> > -		return -ENOENT;
> > -	}
> > +	do { /* 2 iterations: first is to know string length */
> > +		size = length + 1;
> > +		length = snprintf(devargs, size, "%s:%s,%s", busname, devname, drvargs);
> > +		if (length >= size)
> > +			devargs = malloc(length + 1);
> > +		if (devargs == NULL)
> > +			return -ENOMEM;
> > +	} while (size == 0);
> 
> I don't see a good reason for writing it this way.
> You use an additional state (size) and complicate something that is
> pretty straightforward. To make sure no error was written here, I had to
> do step-by-step careful reading, this should not be required by clean
> code.
> 
> You should remove this loop, which then allow removing size, and forces using
> simple code-flow.

The only reason for this loop is to avoid duplicating the snprintf format
in two calls.

It could be replaced by this:

	length = snprintf(devargs, 0, "%s:%s,%s", busname, devname, drvargs);
	if (length < 0)
		return -EINVAL;
	devargs = malloc(length + 1);
	if (devargs == NULL)
		return -ENOMEM;
	snprintf(devargs, length + 1, "%s:%s,%s", busname, devname, drvargs);

Any preference?